1. Field of the Invention
This invention relates to the field of suspensions for disk drives. More particularly, this invention relates to the field of a suspension exhibiting reduced sway-mode gain.
2. Description of Related Art
Dual stage actuated (DSA) suspensions are well known in the hard disk drive (HDD) industry. In a DSA suspension, the suspension is not only activated by a voice coil motor which moves the entire suspension, but an additional microactuator is placed on the suspension itself for effecting fine movements of the head slider located at the distal end of the suspension in order to keep it properly aligned over the data track on the spinning disk. As used herein, the term “proximal” means closer to the end of the suspension that is affixed to the disk drive's actuator arm, and “distal” means closer to the cantilevered end of the suspension. The microactuator(s) provide much finer control and much higher bandwidth of the servo control loop than does the voice coil motor alone, which effects relatively coarse movements of the suspension and hence the magnetic head slider. A piezoelectric element, sometimes referred to simply as a PZT, is often used as the microactuator motor, although other types of microactuator motors are possible. In the discussion that follows, for simplicity the microactuator will sometimes be referred to simply as a “PZT,” although it will be understood that the microactuator need not be of the PZT type.
FIG. 1 is an oblique view of an exemplary prior art disk drive 100 having a DSA suspension with PZTs mounted at the baseplate. The prior art disk drive unit 100 includes a spinning magnetic disk 101 containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The storage medium may be other types of storage medium such as optical storage medium in an optical disk drive, but a magnetic disk drive will be used herein for illustration. The magnetic disk is driven by a drive motor (not shown). Disk drive unit 100 further includes a disk drive suspension 105 to which a magnetic head slider (not shown) which defines a read/write head is mounted proximate a distal end of load beam 107 or other beam portion.
Suspension 105 is coupled to an actuator arm 103, which in turn is coupled to a voice coil motor 112 that moves the suspension 105 arcuately in order to position the head slider over the correct data track on data disk 101 or other recording medium. The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk's surface.
Without admitting that FIG. 2 is “prior art” within the legal meaning of that term, FIG. 2 is a bottom plan view of a prior suspension 10 by the assignee of the present application. As used herein, the “bottom” of a suspension refers to the side of a suspension on which the head slider 42 is mounted, and which faces the spinning data disk platter 101. A bottom view of a suspension is therefore a view of the slider side. The design shown in the figure employs a PZT microactuator 40 extending from a relatively fixed portion of the suspension to the gimbaled area of flexure gimbal assembly 30.
FIG. 3 is a top oblique view of the suspension 10 of FIG. 2. The two PZTs 40 are arranged to rotate head slider 42 about a center of rotation which is ideally located at dimple 18, when the two PZTs 40 are actuated by driving voltages causing one PZT to extend and the other PZT to contract. Because PZTs 40 are disposed near head slider 42 and act more directly upon the slider without having to move the entire load beam and/or part of the base plate, the gimbal-based DSA suspension of FIGS. 2 and 3 provides a higher servo bandwidth as compared to the base plate mounted DSA suspension of FIG. 1.
FIG. 4 is a graph of frequency response functions (FRFs) of the gimbal-based DSA suspension of FIG. 2 according to a simulation. The line labeled “MP FRF” represents the frequency response at the slider 42 when the suspension is activated at the mount plate by the voice coil motor. The line labeled “PZT FRF” represents the frequency response at the slider 42 when the PZTs 40 are activated. The mount plate excited FRF (MP FRF) and the PZT excited FRF (PZT FRF) each have a major peak at approximately 23 kHz. This peak is referred to as the load beam sway mode. To achieve a higher HDD servo bandwidth in the face of a high mode gain, such as a gain exceeding 20 dB, conventional hard disk drive servo controller loops may employ an additional notch design to filter out this high gain.
Although the gimbal-based DSA suspension of FIG. 3 may obtain a cleaner and lower gain PZT FRF in a low frequency range such as below 20 kHz as compared to the suspension of FIG. 1, the sway mode gain in the PZT FRF may still be relatively high. Thus, there is a need for techniques that reduce sway mode gain in gimbal-based DSA suspensions.